The present invention relates generally to seals, and more particularly to a brush seal and to a machine having a brush seal.
Machines include rotary machines such as turbines for steam turbines and compressors and turbines for gas turbines. A steam turbine has a steam path which typically includes, in serial-flow relationship, a steam inlet, a turbine, and a steam outlet. A gas turbine has a gas path which typically includes, in serial-flow relationship, an air intake (or inlet), a compressor, a combustor, a turbine, and a gas outlet (or exhaust nozzle). Gas or steam leakage, either out of the gas or steam path or into the gas or steam path, from an area of higher pressure to an area of lower pressure, is generally undesirable. For example, gas-path leakage in the turbine or compressor area of a gas turbine, between the rotor of the turbine or compressor and the circumferentially surrounding turbine or compressor casing, will lower the efficiency of the gas turbine leading to increased fuel costs. Also, steam-path leakage in the turbine area of a steam turbine, between the rotor of the turbine and the circumferentially surrounding casing, will lower the efficiency of the steam turbine leading to increased fuel costs.
Annular brush seals have been proposed for use between a rotor and a surrounding casing in gas and steam turbines. The annular brush seal is made up of circumferentially-arrayed brush seal segments. Each brush seal segment is attached to the casing and includes a back (i.e., downstream) plate, a front (i.e., upstream) plate, and bristles which are positioned between the back and front plates with the free end of generally each bristle extending beyond the edges of the back and front plates. The bristles typically are canted at an angle of generally forty-five degrees in the direction of rotation of the rotor, and the free ends of the bristles are close to (and may even touch) the rotor. Typically, the front plate (and in some designs also portions of the back plate), near the free ends of the bristles, is spaced apart from the bristles to allow room for the bristles to flex and recover during transient encounters of the free ends of the bristles with the rotor. Metal wire bristles have been proposed with one end of each bristle being welded between and to the front and back plates. Typically, each bristle has a diameter of between 0.002 inch and 0.008 inch. Typically, there are no more than fifteen rows of bristles between the front and back plates because additional rows would make the brush seal too stiff for proper operation and very difficult to manufacture within desired dimensional tolerances. What is needed is an improved brush seal for a machine.
In a first expression of an embodiment of the invention, a brush seal is for reducing leakage of a fluid across a pressure drop in a machine. The brush seal includes a bristle holder attachable to the machine. The brush seal also includes filament yarn bristles secured to the bristle holder. In one construction, the filament yarn is an aramid filament yarn.
In a second expression of an embodiment of the invention, a brush seal is for reducing leakage of a fluid across a pressure drop in a machine. The brush seal includes a bristle holder attachable to the machine. The brush seal also includes yarns, wherein each of the yarns includes filaments, wherein each of the filaments defines a bristle, and wherein each of the bristles is secured to the bristle holder. In one construction, the filaments are aramid filaments.
In a third expression of an embodiment of the invention, a machine includes first and second components, a fluid, and a brush seal. The second component is spaced apart from the first component to define a gap therebetween. The fluid has a pressure drop generally transverse to the gap during machine operation. The brush seal includes a bristle holder attachable to the machine and also includes filament yarn bristles secured to the bristle holder. In one construction, the filament yarn is an aramid filament yarn.
In a fourth expression of an embodiment of the invention, a rotary machine includes a stator, a rotor, a fluid, and a brush seal. The rotor is radially spaced apart from the stator to define a gap therebetween. The fluid has a pressure drop generally transverse to the gap during machine operation. The brush seal includes a bristle holder attachable to the stator. The brush seal also includes yarns, wherein each of the yarns includes filaments, wherein each of the filaments defines a bristle, and wherein each of the bristles is secured to the bristle holder. In one construction, the filaments are aramid filaments.
Several benefits and advantages are derived from the invention. Using aramid filaments for the bristles of a brush seal for a machine results in bristles of smaller diameter resulting in greatly increased bristle packing densities which should significantly reduce leakage. Using a yarn of aramid filaments allows a brush seal of small-diameter bristles to be constructed since it is virtually impossible to handle and secure individual small-diameter aramid filaments to a bristle holder. One example of an aramid filament yarn is a KEVLAR(copyright) (trademark of DuPont) aramid filament yarn. It is noted that making known metal wire or ceramic wire bristles of smaller diameter would result in bristles that would easily break during usage.